Calls for the ban of the rapid-fire gun modification grew louder after mass shootings in Las Vegas and Florida.

The US Department of Justice has submitted a regulation that would ban so-called bump stocks, a type of gun modification that increases the rate of fire for semi-automatic rifles.

The proposal, submitted on Saturday, comes after President Donald Trump announced last month that he was in favour of the ban following a mass shooting in Florida.

"President Trump is absolutely committed to ensuring the safety and security of every American and he has directed us to propose a regulation addressing bump stocks," Attorney General Jeff Sessions said in a statement.

"To that end, the Department of Justice has submitted to the Office of Management and Budget a notice of a proposed regulation to clarify that the National Firearms and Gun Control Act defines "machine gun" to include bump stock type devices," he added.

Under US law, machine guns are officially banned. However, semi-automatic rifles like the AR-15 are legal because of their lower rate of fire.

Bump stocks use the recoil of the semi-automatic rifle to allow the weapon to fire at a higher rate, effectively turning a semi-automatic into a machine gun.

Saturday's proposal would classify bump stocks as part of a "machine gun", making it illegal to buy or sell them.

The proposal must still be approved by the Office of Management and Budget before it is published and subject to a commentary period. It does not, however, require approval from Congress, where it may have faced opposition due the pro-gun ownership lobby's power.

Las Vegas shooting

Bump stocks were heavily criticised last October after one of the deadliest mass shootings in US history.

The gunman, 64-year-old Stephen Paddock, used the modifications to increase his rate of fire, allowing him to kill 58 people at a concert in Las Vegas.

Although Trump announced in October he would be in favour of the ban, no proposal was ever introduced.

The discussion again gained momentum after a gunman opened fire on a Florida high school last month, killing 17 people.

Bump stocks were not used during the Florida shooting, but calls, led by students, for stricter gun control have been heard nationwide.

After February's shooting, Trump said he supported a ban on bump stocks, as well as potentially arming teachers - a proposal that has been criticised by many students and teachers.

On Thursday, state legislators in Florida passed a bill that, among other things, banned bump stocks on a state level.

That state law also rose the minimum age for all gun purchases from 18 to 21.

The bill did not outright ban the sales of AR-15 style assault rifles, which are often used in mass shootings, including both the Florida and Las Vegas shootings. Gun control advocates have long called for such a ban, but so far have not had any success.

Just hours after Florida Governor Scott Pruitt signed the Florida legislation on Friday, the National Rifle Association (NRA) filed a federal lawsuit against the state over the portion of the law that raises the minimum age to buy a firearm.